This invention relates to an oil-cooled piston for internal combustion engines and in particular, to an oil-cooled piston cast in one piece from a cast iron.
It is well known from experience that in heavily stressed engines, the temperature in the top ring groove must not exceed from 180.degree. to 200.degree. C., since otherwise, irrespective of the operational system of the engine, ordinary commercial lubricating oils are likely to evaperate and deposit residues in the piston ring grooves, thus preventing the correct functioning of the same. It is also known that the viscosity of a lubricating oil at 200.degree. C. is so low that it no longer forms an effective lubricating film. Therefore, it is necessary to provide the most effective cooling for the top compression rings in the case of high-stressed plunger pistons.
There have been proposed many kinds of pistons having different piston head structures with cooling chambers formed behind the ring sections of the pistons. Coolent is introduced into the cooling chamber through either the conduit or passage formed in the web section suspending pin bosses from the piston head. Since in the conventional piston passage is formed in the web by machining, the web must be thick enough for the passage to be formed therein, thus resulting in heavy piston which is harmful to piston efficiency and also passage machining itself is time consuming.